Thermal switching devices are known in the prior art which employ coil springs to achieve the desired switching action upon the melting of a thermally-fusible pellet. Employment of a coil spring in such a device, however, makes the device relatively bulky and expensive to produce since the use of an elongated coil spring requires that the device itself have an elongated housing. In many miniature circuit applications it is extremely desirable to utilize more disclike components, especially if such a shape is accompanied by a reduction in the complexity and the component count of the device.
The present invention provides a thermal switch device which has a disclike shape that is achieved by employment of a conductive cup-shaped spring contact which has the pattern cut into its face so that portions of the cup around the pattern are flexible. The thermally-fusible pellet that is used, which melts at a predetermined temperature, presses against a metallic disc which forces the flexible portions of the electrical spring cup into contact with one of the leads of the device until the pellet melts, when the flexible portions of the spring cup move away from this lead. The housing of the thermal switch is in direct contact with the other lead of the device of the present invention to complete the normally closed circuit. In addition, the fixed-location of the spring cup contact of the present invention is capable of presenting a decided simplification and reduction in both size and cost over prior art moving contact devices. Also the structure of the present invention is simpler; and in construction, uses appreciably fewer parts than these devices.